A new benzo[c]carbazolyl-based phosphine ligand has been designed and synthesized. This newly developed ligand efficiently facilitates the Pd-catalyzed tetra-ortho-substituted biaryl syntheses via Suzuki–Miyaura cross-coupling. With 1 mol% of the Pd(OAc)₂/L6 catalyst, sterically congested biaryls were afforded in good-to-excellent yields. In particular, the mild reaction conditions exhibited good compatibility of heterocycles and functional groups including esters and nitrile. L6 was structurally characterized by X-ray crystallographic analysis.